Insights into the Coupled Effects of Fracture Geometry and Sealing on Stimulated Reservoir Volume in Shales

Stimulated reservoir volume (SRV) formed by hydraulic fracturing creates a high-permeability fracture network that concentrates fluid flow in shale gas production. Natural fractures at different scales are instrumental to the formation and enlargement of SRV. In this study, a sensitivity analysis of the impact of fracture geometry on SRV development was performed. In particular, we have considered fracture size, intensity, clustering, and sealing. A typical subsurface formation with background fractures was modeled using an in-house developed discrete fracture network (DFN) software, HatchFrac. Different stochastic distributions were used to describe each geometrical property of the fractures. By dividing two-dimensional (2D) fractures into small segments and three-dimensional (3D) fractures into small blocks, the fracture sealing process was simulated. The Coulomb failure criterion was implemented to identify critically stressed fractures under strike-slip stress conditions. The non-critically stressed and partially open fractures can significantly contribute to shale gas production by increasing SRV. Their contribution depends on the geometrical properties of the fractures. In 2D fracture networks, the probability of open fractures has the greatest impact on the relative increase of SRV. The fracture intensity and length are positively correlated, whereas fractal dimensions and segment lengths are negatively correlated with the relative increase of SRV. Therefore, a greater number of small, open, and clustered fractures yields a larger relative increase of SRV. In 3D fracture networks, the probability of open fractures also significantly impacts the relative increase of SRV. The fracture intensity is positively correlated with the relative increase of SRV, and fracture length and clustering have insignificant impacts.